The present invention relates to tubular containment components for transient containment of molten materials, such as for example only metals and alloys.
Melt processing of reactive, high temperature metals and alloys has created a need for advanced refractory components to contain the molten material during melt processing. Processes such as gas atomization require melt containment components, such as crucibles and pour tubes, that resist attack from molten metals and alloys, which may be superheated. Some molten alloys, such as titanium based alloys, are extremely aggressive towards conventional melt containment materials such as graphite, zirconia and alumina.
Moreover, melt processing applications require the melt containment component to remain free of obstructions from prematurely solidified metal or alloy in order to maintain flow of the melt during processing and to maintain the temperature of the molten material within a selected range. For example, as described in Anderson et al. U.S. Pat. No. 5,125,574, a refractory melt pour tube of a crucible supplies molten metal or alloy to an atomization nozzle and must remain free of obstruction during the atomizing process. The melt pour tube is described as surrounded by a thermally insulating air space to avoid premature freeze-up of the pour tube. The insulating space may have a heat reflector or electrical heating element disposed therein. Moreover, in such gas atomization apparatus, the temperature of the melt at the atomizing nozzle should be controlled to optimize the atomizing process from the standpoint of producing the desired sizes of atomized particles. Cooling of the melt as it flows through the pour tube should be reduced or minimized to this end.
An object of the present invention is to provide an improved tubular refractory melt containment component and method of making same for use in the melt processing of melted materials, such as for example only reactive liquid materials.
The present invention provides a tubular thermal sprayed melt containment component or member for transient containment of molten material wherein the tubular containment member includes a thermal sprayed inner melt-contacting layer for contacting molten metal or alloy to be processed, a thermal sprayed heat-generating material deposited on the inner melt-contacting layer, and an optional thermal sprayed outer thermal insulating layer. In use, the thermal sprayed heat-generating layer is inductively heated as a susceptor of an induction (electromagnetic) field or resistively heated by passing electrical current therethrough. The heat-generating material can comprise the traditional refractory metals such as W, Ta, Mo and alloys thereof one with another and/or with other metals, Nixe2x80x94Cr alloys, iron as well as other metals or alloys or ceramics that can withstand the temperature of the particular melt being processed.
In an illustrative embodiment of the present invention, the thermal sprayed tubular melt containment component pursuant to the present invention comprises an elongated melt supply or pour tube of an atomization apparatus where the melt pour tube supplies molten material from a crucible to an underlying melt atomization nozzle. A refractory metal layer of the pour tube is inductively heated by an induction coil or is resistively heated by connection to an electrical power source during melt atomization.
A thermal sprayed melt containment component or member pursuant to the present invention is made by thermally spraying melt-compatible material on a fugitive mandrel to deposit the inner melt-contacting layer, selectively removing the mandrel, and thermally spraying the heat-generating material on the exterior surface of the inner layer. If used, the outer thermal insulating layer is thermally sprayed on the heat-generating layer.